High fidelity sheet explosive simulants

ABSTRACT

An explosive sheet simulant that uses an ethylene vinyl acetate polymer combined with either a mixture of a boron carbide and iron oxide for X-ray attenuating properties or calcium carbonate for millimeter wave properties, wherein the components of the mixture are selected such that the sheet has a predetermined flexural modulus combined with particle density, effective atomic number, x-ray transmission properties, or millimeter wave properties.

BACKGROUND Field of the Disclosure

This application relates generally to improvements to explosivesimulants. More particularly the present disclosure relates toimprovements relating to polymer based sheet simulants for explosivedetection systems that use advanced image technologies.

Description of the Related Art

Explosive simulants are commonly used to field test various explosivedetection systems and to train operators of such equipment. Explosivesimulants are largely designed for X-ray imaging and explosive detectionsystem (EDS) platforms, where a simulant's X-ray parameters are matchedto those of an explosive. The EDS is commonly used to identifyexplosives in luggage and not particularly those on a human. However,the EDS lack focus on aspects such as edge effects, compressibility, andflexibility of an explosive. Generalizations are made for matchingsimulant and explosive morphology, but little has been done to determinethe effect morphology has on AIT detection algorithms and to validatethe morphology between an explosive and simulant. Tactile propertieshave not been as critical in EDS simulant development compared to thedevelopment of simulants used for more advanced explosive detectionsystems, such as Advanced Imaging Technology (AIT) portals.

Both X-ray backscatter and MMW based AIT portals require validatedsimulants for testing and development. MMW simulants are conceptuallydeveloped in a similar manner as X-ray simulants. However, differenttechnologies are used for measuring and validating the materials. Whenused in MMW based AIT portals, simulants and explosives with similardielectric properties produce similar grayscale responses. Regardless ofthe MMW dielectric response or the X-ray backscatter response, the AITalgorithm threat detection relies heavily upon anomaly identification.AIT portals use detection algorithms that rely heavily on anomalydetection algorithms. Therefore, it is imperative that simulants mimicand behave in a manner similar to that of the actual explosive that thesimulant is meant to simulate. As such, when developing simulants forAIT portals, there is an ever increasing need for simulants to match theflexural properties of explosives in order for the simulants to beindistinguishable from live explosives. AIT portals use two distincttechnologies: backscatter X-rays and millimeter wave (MMW) scanning.

SUMMARY

According to an embodiment of the present disclosure, there is provideda first explosive simulant. The explosive simulant includes a sheetincluding a mixture of a boron carbide, an iron oxide, and an ethylenevinyl acetate polymer, in which the components of the mixture areselected such that the sheet has a predetermined flexural modulus,particle density, effective atomic number, and x-ray transmissionproperties.

Further, according to an embodiment of the present disclosure there isprovided a second explosive simulant. The second explosive simulantincludes a sheet including a mixture of a calcium carbonate and anethylene vinyl acetate polymer, wherein the components of the mixtureare selected such that the sheet has a predetermined flexural modulus,and millimeter wave properties.

Further, according to an embodiment of the present disclosure, there isprovided a method for manufacturing a simulant that imitates theproperties of an explosive. The method includes melting and blendingethylene vinyl acetate polymer including a naphthenic plasticizer,adding specific amount of particulate chemicals selected from a groupcomprising of boron carbide, iron oxide, and calcium carbonate in smallincrements and mixing to form a uniform mixture, and pouring the uniformmixture in a tray and baking the uniform mixture in a laboratory oven.

The forgoing general description of the illustrative implementations andthe following detailed description thereof are merely exemplary aspectsof the teachings of this disclosure, and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate one or more embodiments and,together with the description, explain these embodiments. Theaccompanying drawings have not necessarily been drawn to scale. Anyvalues or dimensions illustrated in the accompanying graphs and figuresare for illustration purposes only and may or may not represent actualor preferred values or dimensions. Where applicable, some or allfeatures may not be illustrated to assist in the description ofunderlying features. In the drawings:

FIG. 1 is a flow chart of the manufacturing process of an explosivesimulant according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

The description set forth below in connection with the appended drawingsis intended as a description of various embodiments of the disclosedsubject matter and is not necessarily intended to represent the onlyembodiment(s). In certain instances, the description includes specificdetails for the purpose of providing an understanding of the disclosedembodiment(s). However, it will be apparent to those skilled in the artthat the disclosed embodiment(s) may be practiced without those specificdetails. In some instances, well-known structures and components may beshown in block diagram form in order to avoid obscuring the concepts ofthe disclosed subject matter.

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with an embodiment is included inat least one embodiment of the subject matter disclosed. Thus, theappearance of the phrases “in one embodiment” or “in an embodiment” invarious places throughout the specification does not necessarily referto the same embodiment. Further, the particular features, structures orcharacteristics may be combined in any suitable manner in one or moreembodiments. Further, it is intended that embodiments of the disclosedsubject matter cover modifications and variations thereof.

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context expressly dictates otherwise. That is, unlessexpressly specified otherwise, as used herein the words “a,” “an,”“the,” and the like carry the meaning of “one or more.” Furthermore,terms such as “first,” “second,” “third,” etc., merely identify one of anumber of portions, components, steps, operations, functions, and/orpoints of reference as disclosed herein, and likewise do not necessarilylimit embodiments of the present disclosure to any particularconfiguration or orientation.

Furthermore, the terms “approximately,” “proximate,” “minor,” andsimilar terms generally refer to ranges that include the identifiedvalue within a margin of 20%, 10% or preferably 5% in certainembodiments, and any values there between.

Explosive detection systems (EDSs) are machines that use a combinationof X-ray scanning and image processing to scan luggage bags and otheritems to identify the densities and patterns correlating to an explosiveor chunks of explosives. Advanced Imaging Technology (AIT) portals scanhumans to determine if objects are hidden under their clothing. In orderto test and validate these systems, weapons, explosives and simulantsare utilized. Simulants for EDS technologies are mainly developed tomatch the X-ray attenuation properties of the actual explosives, whereassimulants developed for AIT portals are developed to match the scatterand reflectance of either the X-ray or millimeter wave (MMW) propertiesof the actual explosives.

In one embodiment of the present disclosure, explosive simulants aremanufactured for a PETN based sheet explosive (also referred as PETNsheet explosive 2 in table 1). The simulant is initially developedtargeting the X-ray properties listed in table 1 followed by theflexural property shown in Table 2. The flexural property relates to thetendency of a material to bend and is typically characterized bycalculating the flexural modulus of a material. Further, additionalcharacteristics that can be matched include physical form, x-raytransmission properties, mass density, effective atomic number Z, andtactile properties. The characteristics of the first explosive simulantare compared with the PETN sheet explosive 2 in Table 1.

TABLE 1 Properties of the first explosive simulant PETN Sheet X-rayproperties Explosive 2 New Simulant Tolerance* Density (g/cc) 1.48 1.50±0.02 Z effective 7.81 7.76 ±0.15 High Reveal-CT# 13801 13403 N/A LowReveal-CT# 13692 13390 N/A In Table 1, *indicates that the densitytolerance was set at 1: 0.02 g/cc based on the inherent range ofvariation found in commercial and military explosives. CT Number isexpressed in Modified Hounsfield Units and is used for comparison, as notolerance threshold has been established.

The present disclosure focuses on matching the flexural properties of asheet explosive as measured on an Instron Universal Test Machine 3342using a 3-point flex modulus test. Initial flexural modulus tests areperformed on a standardized sample of the sheet explosive to determinethe target flexural value. The measured flex modulus quantifies theresistance to a bending force of the sheet explosive and provides thetarget value for the simulant to match. Simulant development begins withthree commercial products of pre-blended Ethylene Vinyl Acetate (EVA)and plasticizer mixed together. The products contain different levels ofEVA and plasticizer and by adjusting the relative amounts; you cancontrol the flex modulus of the simulant polymer base. When you increasethe amount of plasticizer, the flex modulus goes down. When you lowerthe amount of plasticizer, the flex modulus increases (i.e. the samplebecomes stiffer and more resistant to bending force). An arbitraryamount of polymer base is then loaded with a fixed amount of solids thatwill control the X-ray or dielectric properties to match those of theexplosive sample. The addition of solids to the polymer base willincrease the flex modulus of the overall mixture. A standardized sampleof the first simulant prototype formula is tested for flex modulusaccording the same method used to test the explosive. The results of thesimulant and explosive are compared, and depending on the results, thepolymer base of the simulant prototype is then adjusted to eitherincrease or decrease the flex modulus in order to compensate for thesolids. This is repeated in an iterative process until the target flexmodulus is achieved.

The first explosive simulant is a mixture of two or more non-explosivecomponents. In one embodiment, the first explosive simulant includes57.2% boron carbide with 1.9% iron oxide, suspended in 40.9% ethylenevinyl acetate polymer; specifically 34.9% HB-218 and 6.0% HS-103. Otherformulation ingredients may include, but are not limited to, BoronCarbide 49.0-71.0%, Iron Oxide: 0.7-2.5%, Polymer 230: 10.0-34.0%,Polymer 218: 10.0-58.0%, and Polymer 103: 6.0-34.0%. Furthermore, acertain percentage of HB-230 can also be added to the mixture. Polymerblends HS-103, HB-218, and HB-230 are exemplary compounds and othercompounds with similar properties can be used. The properties thatshould be satisfied may include, but are not limited to, density,Z-effective, MAC, electron density, Z-e, (Nitrogen plus Oxygen) to(Carbon plus Hydrogen) ratio, dielectric constant, millimeter wavereflectivity, and flexural modulus. The first explosive simulant hasX-ray properties are consistent with the PETN sheet explosive 2, asshown in Table 1. Further, the flexural modulus of the first explosivesimulant is approximately equal to those of the PETN sheet explosivesand RDX sheet explosives, as illustrated in Table 2.

Additionally, as depicted in Table 2, characterization of four differentsheet explosives as well as three commercially available sheet explosivesimulants was also performed to differentiate the first explosivesimulant (referred to as “new simulant” in Table 2) of the presentdisclosure from the rest. According to the present disclosure, the testutilized a 5.08 cm×7.62 cm sample aliquot taken from a larger samplelot. The specimens were tested only once prior to being discarded. Aminimum of ten samples were measured for repeatability purposes. Asshown in Table 2, the first explosive simulant, according to anembodiment of the present disclosure, has proven to be a vastimprovement over the commercially available sheet explosive simulants.The first explosive simulant also successfully reproduced the targetedX-ray properties of the explosive.

TABLE 2 Flexural Modulus comparison with the first explosive simulant(New Simulant) Explosives Flexural PETN Sheet RDX Sheet Simulantsmodulus Explosive Explosive Commercial Product New (ksi) 1 2 1 2 1 2 3Simulant Average 0.307 0.216 0.481 0.241 2.377 2.925 1.770 0.493Standard 0.043 0.020 0.062 0.023 0.118 0.160 0.073 0.064 deviation

The ability to control the flexural modulus is important for thedevelopment of new categories of explosive simulants for AIT systems,which significantly rely on physical characteristics. The AIT portals'detection algorithms identify anomalies by examining image contrast,edge effects, and image irregularities. A crucial characteristic forexplosive simulants for AIT systems is the ability to conform to a humanbody in the same manner as that of actual explosives, so that thedetection algorithm may not easily discern a given explosive from thebackground. Additionally, another crucial characteristic in simulantdevelopment for AITs is that the explosive simulant also matches theproperties of the actual explosive as determined by the AIT system'stechnology platform (X-ray or MMW).

Two main types of AIT technologies exist, X-ray based and MMW based. Thesimulants for X-ray based AIT technologies are developed by matching theX-ray properties of the simulants to those of the actual explosive. Onthe other hand, simulants for MMW based AIT technologies are developedby matching the actual explosive's dielectric response.

In one embodiment of the present disclosure, a second explosive simulantmatching the MMW dielectric response and flexural modulus of theexplosive is developed. The second explosive simulant formula includes42.8% calcium carbonate suspended in 57.2% HS-218 ethylene vinyl acetatepolymer blend. Other formulation ingredients may include, but are notlimited to, Polymer 230: 10.0-34.0%, Polymer 218: 10.0-58.0%, Polymer103: 6.0-34.0%, and Calcium Carbonate: 38-48%. Table 3 illustrates thatthe second explosive simulant (referred as MMW sheet simulant in table3) exhibited dielectric properties similar to those of the PETN sheetexplosive 2. The real permittivity ε′ of the PETN Sheet Explosive 2 andthe second explosive simulant are also approximately the same. Inaddition, the flexural moduli of the two are also approximately similar.

TABLE 3 MMW Sheet Simulant Results Real Imaginary Flexural ModulusSample ε′ ε″ (ksi) PETN Sheet Explosive 2 2.82 0.16 0.216 MMW SheetSimulant 2.77 0.01 0.190

The first explosive simulant and the second explosive simulant can bemanufactured in a similar manner as illustrated in FIG. 1.

FIG. 1 illustrates the manufacturing process of an explosive simulantaccording to an embodiment of the present disclosure. In step 101, theethylene vinyl acetate (EVA) polymer containing a naphthenic plasticizeris melted and blended by applying compression, such as using a two-rollmill machine. The plasticizer renders the mixture easier to process incalendaring, tubing, and embossing operations. It also renders themixture more plastic for shaping operations. In step 303, specificamounts of particulate chemicals (such as boron carbide, iron oxide, andcalcium carbonate) are added in small increments and are mixed uniformlywith the EVA to produce a mixture that achieves a target density andZ-effective. In step 105, the mixture is poured into a tray or mold andplaced in a laboratory oven for baking. During the baking process, themixture flows into a sheet of predetermined thickness, due to gravity.The baking process may be visually observed and the baking (applicationof heat/temperature) may be stopped when the mixture forms into a sheet.The area and thickness of the sheet is determined by the dimensions ofthe tray or mold. The baking may be performed at various temperaturesfor different ranges of time. For example, the oven can be set to 115°C. and baking can be carried out for 10 minutes while varyingtemperatures of 105-130° C. and times of 10-120 minutes being found tobe acceptable when varying the amount of material being manufactured.

To produce higher density sheet explosive simulants, the composition ofthe polymer with naphthenic plasticizer may need to be altered toachieve the desired density while remaining cross linked. The change inthe polymer blend results in the ability to add a larger concentrationof particle matter, in addition to being more flexible. A final set offifty-six (56) parametric sheets were produced, each sheet measuring38×25×0.5 cm and covering a density range from 1.40 to 1.75 andZ-effective range of 7.00 to 8.50. The flexibility of the sheets, due tothe variation of polymer blends in the sheets.

Commercially available sheet explosive simulants are predominantlydesigned for matching the X-ray properties of an actual explosive.Furthermore, they rarely incorporate the tactile properties and flexuralproperties of the explosive into the attributes of the explosivesimulant. If the flexibility of an explosive simulant does notadequately match that of the actual explosive that the simulant is meantto simulate, there could be effects on the shape and packaging of theexplosive simulant that lead to differences in the images obtained fromAIT portals. This may potentially lead to erroneous conclusions from AITtesting. For instance, a stiff rectangular shaped simulant cannotconform to the curvature of human body, and as such can be easilyidentified by the AIT portal unlike an actual explosive that doesconform. Characterizing the physical flexural properties of an explosiveand incorporating those parameters into the explosive simulant providesanother layer of fidelity, creating an explosive simulant that is nearlyidentical to the actual explosive (except for its blast properties) asdetected by a scanning technology. This addition of mimicking anexplosive's flexibility directly affects the correlation betweenmaterial properties and AIT threat detection algorithms. Otherwise, ifthe simulant and explosive differ in flexibility the AIT's detectionresponse may be different because of the morphology effects, e.g., edgeeffects or stiffness

In one embodiment, the explosive simulants are designed to withstandmultiple uses involving significant bending. In contrast, explosives aregenerally designed to be used once. Therefore, the explosive simulantsmanufactured according to the process in FIG. 1 in the presentdisclosure are advantageous because the flexural modulus can be modifiedsuch that the explosive simulants has significantly better flexuralproperties than the explosive. The development of an extremely flexibleexplosive simulant specifically for testing detection systems could bebeneficial in pushing the boundaries of detection and identifyingpossible vulnerabilities of the system and detection algorithms.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the present disclosures. Indeed, the novel methods, apparatusesand systems described herein can be embodied in a variety of otherforms. Furthermore, various omissions, substitutions and changes in theform of the methods and apparatuses described herein can be made withoutdeparting from the spirit of the present disclosures. The accompanyingclaims and their equivalents are intended to cover such forms ormodifications as would fall within the scope and spirit of the presentdisclosures.

What is claimed is:
 1. An explosive simulant, consisting of a mixtureof: 52.0-62.0% ethylene vinyl acetate (EVA) polymer; and 38-48% calciumcarbonate, wherein the explosive simulant is in a form of a sheet havingpredetermined flexural modulus and millimeter wave properties.
 2. Theexplosive simulant according to claim 1, wherein the flexural modulusand millimeter wave properties is approximately equal to that ofpentaerythritol tetranitrate (PETN) or cyclotrimethylenetrinitramine(RDX) sheet explosive.
 3. A method for manufacturing the explosivesimulant of claim 1, the method comprising: melting and blending anamount of ethylene vinyl acetate (EVA) polymer; adding to the EVA anamount calcium carbonate, and mixing to form a uniform mixture; andpouring the uniform mixture into a tray or mold and heating until asheet is formed, wherein the sheet has predetermined flexural modulusand millimeter wave properties.
 4. The method according to claim 3,wherein the explosive simulant consists of 38-48% calcium carbonate and52.0-62.0% EVA polymer.
 5. The method according to claim 3, wherein themelting and blending is achieved by using a two-roll mill machine orother pressure mixing operation.
 6. The method according to claim 3,wherein the uniform mixture in the tray or mold is heated at atemperature of 105° C.-130° C. for 10-120 minutes.
 7. The methodaccording to claim 3, wherein the sheet has flexural modulus andmillimeter wave properties approximately equal to that ofpentaerythritol tetranitrate (PETN) or cyclotrimethylenetrinitramine(RDX) sheet explosive.